Organic solar cell and method of manufacturing the same

ABSTRACT

An organic solar cell and a method of manufacturing the same.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No.10-2010-0098997, filed on Oct. 11, 2010, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organic solar cell and a method ofmanufacturing the same.

2. Description of the Related Art

Amid rising interests in renewable energy increasing worldwide, organicsolar cells are currently drawing attention as a promising future energysource having a variety of advantages.

Compared with inorganic solar cells using silicon, organic solar cellsmay be manufactured as a thin film at low cost and may be applicable tovarious types of flexible devices.

Therefore, to further improve characteristics of organic solar cellsresearch and development have been conducted in respect to variousaspects. As an example, attempts have been made to improvecharacteristics of a photoactive layer of an organic solar cell bythermal treatment of a photoactive layer material, surface treatment ofthe photoactive layer, or the like.

However, improvement of a photoelectric conversion efficiency of theorganic solar cell and reduction of manufacturing costs are stillnecessary.

SUMMARY OF THE INVENTION

The present invention relates to an organic solar cell that may beimplemented at low cost, and a method of manufacturing the organic solarcell.

According to an aspect of the present invention, there is provided anorganic solar cell including: a first electrode; a second electrode; aphotoactive layer disposed between the first electrode and the secondelectrode; and an electron extraction layer disposed between thephotoactive layer and the second electrode, wherein the electronextraction layer comprises an ionic polymer.

The ionic polymer may include at least one substituent represented byFormula 1A below:

wherein, in Formula 1A, a is an integer from 0 to 30;

L₁ is —O—, a substituted unsubstituted C₁-C₁₀ alkylene group, asubstituted or unsubstituted C₂-C₁₀ alkenylene group, a substituted orunsubstituted C₆-C₂₀ arylene group, or a substituted or unsubstitutedC₃-C₂₀ heteroarylene group;

p is an integer from 1 to 10;

A₁ is —CO₂M₁, —SO₃M₁, or —PO₃M₁M₂; and

M₁ and M₂ are each independently a monovalent cation.

L₁ in Formula 1A may be —O—, a methylene group, an ethylene group, apropylene group, a butylene group, a phenylene group, a naphthylenegroup, or an anthrylene group.

M₁ and M₂ in Formula 1A may be each independently a hydrogen atom or analkaline metal.

The substituent represented by Formula 1A may be a substituentrepresented by one of Formulae 10A to 10E below:

wherein, in Formulae 10A to 10E, M₁ is H, Li, Na, or K.

The ionic polymer may include at least one of a repeating unitrepresented by Formula 2A below, a repeating unit represented by Formula3A below, a repeating unit represented by Formula 4A below, a repeatingunit represented by Formula 5A below, a repeating unit represented byFormula 6A below, and a repeating unit represented by Formula 7A below:

wherein, in Formulae 2A to 7A, Ar₁ to Ar₃ are each independently aC₁-C₃₀ alkylene group, a C₆-C₃₀ arylene group, a C₃-C₃₀ heteroarylenegroup, a C₅-C₃₀ cycloalkylene group, a C₁-C₃₀ alkylene group substitutedwith at least one first group, a C₆-C₃₀ arylene group substituted withat least one second group, a C₃-C₃₀ heteroarylene group substituted withat least one third group, or a C₅-C₃₀ cycloalkylene group substitutedwith at least one fourth group;

b to d are each independently an integer from 1 to 20; and

R₁ to R₄, R₁₁, R₁₃, R₁₄, R₁₅, the first group, the second group, thethird group, and the fourth group are each independently a hydrogen atom(H), a nitro group (—NO₂), a cyano group (—CN), a hydroxyl group (—OH),a halogen atom, a substituted or unsubstituted C₁-C₃₀ alkyl group, asubstituted or unsubstituted C₁-C₃₀ alkoxy group, a substituted orunsubstituted C₆-C₃₀ aryl group, a substituted or unsubstituted C₆-C₃₀arylalkyl group, a substituted or unsubstituted C₆-C₃₀ aryloxy group, asubstituted or unsubstituted C₂-C₃₀ heteroaryl group, a substituted orunsubstituted C₂-C₃₀ heteroarylalkyl group, a substituted orunsubstituted C₂-C₃₀ heteroaryloxy group, a substituted or unsubstitutedC₅-C₂₀ cycloalkyl group, a substituted or unsubstituted C₂-C₃₀heterocycloalkyl group, a substituted or unsubstituted C₁-C₃₀ alkylestergroup, a substituted or unsubstituted C₆-C₃₀ arylester group, asubstituted or unsubstituted C₂-C₃₀ heteroarylester group, —N(Q₁)(Q₂),—C(═O)—NH₂, or a substituent represented by Formula 1A below, wherein Q₁to Q₂ are each independently a hydrogen atom, a C₁-C₃₀alkyl group, aC₆-C₃₀ aryl group, or a C₂-C₃₀ heteroaryl group, and at least one of R₁to R₄, R₁₁, R₁₃, R₁₄, R₁₅, the first group, the second group, the thirdgroup, and the fourth group is a substituent represented by Formula 1Aabove.

The ionic polymer may include a repeating unit represented by Formula 8Abelow with a terminal to which a substituent represented by Formula 1Aabove:

wherein, in Formula 8A, R₂₁ to R₂₄ are each independently a hydrogenatom (H), a nitro group (—NO₂), a cyano group (—CN), a hydroxyl group(—OH), a halogen atom, a substituted or unsubstituted C₁-C₃₀ alkylgroup, a substituted or unsubstituted C₁-C₃₀ alkoxy group, a substitutedor unsubstituted C₆-C₃₀ aryl group, a substituted or unsubstitutedC₆-C₃₀ arylalkyl group, a substituted or unsubstituted C₆-C₃₀ aryloxygroup, a substituted or unsubstituted C₂-C₃₀ heteroaryl group, asubstituted or unsubstituted C₂-C₃₀ heteroarylalkyl group, a substitutedor unsubstituted C₂-C₃₀ heteroaryloxy group, a substituted orunsubstituted C₅-C₂₀ cycloalkyl group, a substituted or unsubstitutedC₂-C₃₀ heterocycloalkyl group, a substituted or unsubstituted C₁-C₃₀alkylester group, a substituted or unsubstituted C₆-C₃₀ arylester group,a substituted or unsubstituted C₂-C₃₀ heteroarylester group, —N(Q₁)(Q₂),or —C(═O)—NH₂, wherein Q₁ to Q₂ are each independently a hydrogen atom,a C₁-C₃₀ alkyl group, a C₆-C₃₀ aryl group, or a C₂-C₃₀ heteroaryl group.

The ionic polymer may have a weight average molecular weight (Mw) offrom about 1,000 to about 90,000,000.

The electron extraction layer may have a thickness of from about 0.1 nmto about 10 nm.

One surface of the electron extraction layer and one surface of thesecond electrode may contact each other.

According to another aspect of the present invention, there is provideda method of manufacturing an organic solar cell, the method including:forming a first electrode on a substrate; forming a photoactive layer onthe first electrode; forming an electron extraction layer comprising anionic polymer on the photoactive layer; and forming a second electrodeon the electron extraction layer, wherein the forming of the electronextraction layer may include forming a first layer from a mixture of theionic polymer and a solvent; and removing at least part of the solventfrom the first layer to obtain the electron extraction layer.

The forming of the first layer in the forming of the electron extractionlayer may be performed using spin coating, inkjet printing, nozzleprinting, dip coating, electrophoresis, tape casting, screen printing,doctor blade coating, gravure printing, gravure offset printing, aLangmuir-Blogett method, or a layer-by-layer self-assembly method.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawing in which:

FIG. 1 is a schematic cross-sectional view of an organic solar cellaccording to an embodiment of the present invention;

FIG. 2 is an energy level diagram of each layer of the organic solarcell of FIG. 1; and

FIG. 3 is a graph illustrating the voltage-current characteristics oforganic solar cells manufactured according to Example 1 and ComparativeExample 1, respectively.

DETAILED DESCRIPTION OF THE INVENTION

The present disclosure will now be described more fully with referenceto the accompanying drawings, in which exemplary embodiments of thepresent disclosure are shown.

FIG. 1 is a schematic cross-sectional view of an organic solar cellaccording to an embodiment of the present disclosure. Referring to FIG.1, the organic solar cell according to the present embodiment includes afirst electrode 101, a hole extraction layer 102, a photoactive layer104, an electron extraction layer 106, and a second electrode 108, whichare sequentially stacked in the stated order.

The first electrode 101 may be formed on a substrate (not shown). Thesubstrate may be a substrate (for example, a silicon substrate and thelike) used in general semiconductor manufacturing processes or asubstrate made of a substantially transparent material (colorless andtransparent, colored transparent, or translucent) that allows externallight such as solar light to pass therethrough. Examples of thesubstrate include glass substrates, metal oxide substrates, and polymersubstrates. Non-limiting examples of metal oxides for the substrateinclude aluminum oxide, molybdenum oxide, and indium tin oxide.Non-limiting examples of polymers for the substrate includepolyethersulphone (PES), polyacrylate (PAR), polyetherimide (PEI),polyethylene napthalate (PEN), polyethylene terepthalate (PET),polyphenylene sulfide (PPS), polyallylate, polyimide, polycarbonate(PC), cellulose triacetate (TAC), and cellulose acetate propinonate(CAP). The substrate may have a single layer structure consisting of amixture of at least one material, and in another embodiment, may have amulti-layer structure including a stack of layers, each consisting of atleast two kinds of materials.

The first electrode 101 may be an anode. A material for the firstelectrode 101 may have a high work function. Examples of the materialfor the first electrode 101 include transparent and highly conductivematerials, such as indium tin oxide (ITO), indium zinc oxide (IZO), tinoxide (SnO₂), zinc oxide (ZnO), fluorine tin oxide (FTO), and antimonytin oxide (ATO). Other examples of the material for the first electrode13 include magnesium (Mg), aluminum (Al), platinum (Pt), silver (Ag),gold (Au), copper (Cu), molybdenum (Mo), titanium (Ti), tantalum (Ta), acombination of at least two thereof (for example, an alloy thereof,aluminum-lithium, calcium (Ca), magnesium-indium (Mg—In), ormagnesium-silver (Mg—Ag), which may be in a co-deposition layer), andcarbonaceous materials such as graphite. The first electrode 101 mayinclude two different materials. The first electrode 101 may have any ofvarious structures, and in some embodiments, may have a double-layerstructure including two different materials. The first electrode 101 maybe formed using any of various known methods, for example, sputtering,deposition (vapor deposition, thermal deposition, or the like), ion beamassisted deposition (IBAD), or wet coating, which are selected dependingon the material for the first electrolyte 101.

The hole extraction layer 102 may be disposed on the first electrode101. The hole extraction layer 102 may capture holes generated in thephotoactive layer 104 and transfer them to the first electrode 101.

A material for the hole extraction layer 102 may be a conductivepolymer. Non-limiting examples of the conductive polymer includePEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)),polyaniline, polydiphenyl, acetylene, poly(t-butyl)diphenylacetylene,poly(trifluoromethyl)diphenylacetylene, Cu-PC (copper phthalocyanine)poly(bistrifluoromethyl)acetylene, polybis(T-butyldiphenyl)acetylene,poly(trimethylsilyl)diphenylacetylene, poly(carbazole)diphenylacetylene,polydiacetylene, polyphenylacetylene, polypyridineacetylene,polymethoxyphenylacetylene, polymethylphenylacetylene,poly(t-butyl)phenylacetylene, polynitrophenylacetylene,poly(trifluoromethyl)phenylacetylene,poly(trimethylsilyl)phenylacetylene, derivatives thereof, and acombination of at least two thereof.

For example, the material for the hole extraction layer 102 may bePEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)).

The hole extraction layer 102 may be formed using any of various knownmethods, for example, deposition (vapor deposition, thermal deposition,or the like), ion beam assisted deposition (IBAD), or wet coating, whichare selected depending on the material for the hole extraction layer102.

The hole extraction layer 102 may have a thickness of from about 1 nm toabout 500 nm. When the thickness of the hole extraction layer 102 iswithin this range, the hole extraction layer 102 may exhibit good holeextraction performance without a substantial increase in drivingvoltage.

The photoactive layer 104 may be disposed on the hole extraction layer102. The photoactive layer 104 may generate holes and electrons byabsorbing external light such as solar light.

The photoactive layer 104 may have any of a variety of structures, forexample, a single layer structure including an electron donor materialand an electron acceptor material, or a multi-layer structure includingan electron donor material-containing layer and an electron acceptormaterial-containing layer.

The electron donor material may be a p-type conductive polymer materialincluding a π-electron. Non-limiting examples of the conductive polymeras an electron donor material include P3HT (poly(3-hexylthiophene)),polysiloxane carbazole, polyaniline, polyethylene oxide,(poly(1-methoxy-4-(O-disperse red1)-2,5-phenylene-vinylene), MEH-PPV(poly-[2-methoxy-5-(2′-ethoxyhexyloxy)-1,4-phenylene vinylene]);MDMO-PPV (poly[2-methoxy-5-3(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene]); PFDTBT(poly(2,7-(9,9-dioctyl)-fluorene-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole));PCPDTBT(poly[N′,0′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiazole)],PCDTBT(poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)])polyindole,polycarbazole, polypyridiazine, polyisothianaphthalene, polyphenylenesulfide, polyvinylpyridine, polythiophene, polyfluorene, polypyridine,and derivatives thereof. Any combination of at least two of theabove-listed electron donor materials, for example, as a blend or acopolymer, may be used.

Non-limiting examples of the electron acceptor material includefullerene, a derivative thereof (for example, PCBM ([6,6]-phenyl-C61butyric acid methyl ester)), nanocrystals such as CdSe, carbonnanotubes, polybenzimidazole (FBI) nanorods, and3,4,9,10-perylenetetracarboxylic bisbenzimidazole (PTCBI).

The photoactive layer 104 may be a single layer including P3HT as anelectron donor material, and fullerene derivative PCBM ([6,6]-phenyl-C61butyric acid methyl ester) as an electron acceptor material, but is notlimited thereto.

When the photoactive layer 104 includes a mixture of an electron donormaterial and an electron acceptor material, a mixing ratio of theelectron donor material to the electron acceptor material may be from10:1 to 10:100 by weight, but is not limited thereto.

The photoactive layer 104 may have a thickness of, for example, fromabout 10 nm to about 2000 nm. The photoactive layer 104 may be formedusing a general deposition method or a coating method, for example,using spraying, spin coating, dipping, printing, a doctor blade method,sputtering, or electrophoresis. However, any appropriate method may beused.

The electron extraction layer 106 may be disposed on the photoactivelayer 104. The electron extraction layer 106 may capture electronsgenerated in the photoactive layer 104 and transfer them to the secondelectrode 108.

The electron extraction layer 106 may include an ionic polymer. As aresult, an increased difference in work function between the firstelectrode 101 and the second electrode 108 may lead to an increased opencircuit voltage (V_(OC)) of an organic solar cell, thus facilitatingmigration of electrons from the photoactive layer 104 to the secondelectrode 108 and resulting in an increased short circuit current(J_(SC)). Therefore, the organic solar cell with the electron extractionlayer 106 including the ionic polymer may have an improved photoelectricconversion efficiency.

FIG. 2 is an energy level diagram of each layer of the organic solarcell in FIG. 1, illustrating an energy level 201 of the first electrode101, a highest occupied molecular orbital (HOMO) 214 of an electrondonor material 204 a in the photoactive layer 104, a lowest unoccupiedmolecular orbital (LUMO) 224 of an electron acceptor material 204 b inthe photoactive layer 104, and an energy level 208 of the secondelectrode 108. Although the energy level of the photoactive layer 104 isillustrated separately for a layer containing the electron donormaterial 204 a and a layer containing the electron acceptor material 204b, the photoactive layer 104 of FIG. 2 is not limited to having a doublelayer structure including the electron donor material-containing layerand the electron acceptor-containing layer. For convenience ofillustration, an energy level of the hole extraction layer 102 is notillustrated in FIG. 2.

Referring to FIGS. 1 and 2, holes generated in the photoactive layer 104of the organic solar cell by exposure to external light such as solarlight migrate to the first electrode 101 from the HOMO 214 of theelectron donor material 204 a, while electrons generated in thephotoactive layer 104 migrate from the LUMO 224 of the electron acceptormaterial 204 b to the second electrode 108 via the electron extractionlayer 106.

The inclusion of the ionic polymer in the electron extraction layer 106may cause formation of a “dipole layer” including a positive chargeregion (δ+) and a negative charge region (δ−), as illustrated in FIG. 2,so that a vacuum energy level (denoted by dotted lines 206 in FIG. 2)may be shifted upward. This may result in an increased difference inwork function between the first electrode 101 and the second electrode108, and thus an increased open circuit voltage of the organic solarcell. In some embodiments the vacuum energy level may be shifted aboveby 0.05 eV or greater. However, the present disclosure is not limitedthereto.

The shift of the vacuum energy level (see the dotted line 206 of FIG. 2)may reduce the difference in work function between the LUMO 224 of thephotoactive layer 104 and the second electrode 108 to facilitate thetransfer of electrons generated in the photoactive layer 104 to thesecond electrode 108. Thus, the organic solar cell may have an increasedshort circuit current.

The ionic polymer in the electron extraction layer 106 may have a dipolemoment of 0.3 debye or greater, and in some embodiments, may have adipole moment of about 0.36 debye to about 12 debye. These data weremeasured using toluene as a solvent at about 38.4° C. When the ionicpolymer in the electron extraction layer 106 has a dipole moment withinthese ranges, such a shift in vacuum energy level as illustrated in FIG.2 (denoted by the dotted line 206 in FIG. 2) may be facilitated.

The ionic polymer may include at least one substituent represented byFormula 1A:

In Formula 1A, a may be an integer from 0 to 30. In some embodiments, ifa is 0, A₁ may be directly linked to a main chain of the ionic polymer.a may be an integer randomly selected from among 0 to 30.

In Formula 1A, L₁ may be —O—, a substituted or unsubstituted C₁-C₁₀alkylene group, a substituted or unsubstituted C₂-C₁₀ alkenylene group,a substituted or unsubstituted C₆-C₂₀ arylene group, or a substituted orunsubstituted C₃-C₂₀ heteroarylene group. For example, L₁ may be —O—, aC₁-C₅ alkylene group, a C₂-C₅ alkenylene group, a C₆-C₁₄ arylene group,or a C₂-C₁₄ heteroarylene group. For example, L₁ may be —O—, a methylenegroup, an ethylene group, a propylene group, a butylene group, aphenylene group, a naphthylene group, or an anthrylene group, but is notlimited thereto. In some embodiments, if a is 2, L₁ may be —O— or apropylene group.

In Formula 1A, p is an integer from 1 to 10. p may depend on L₁. Forexample, p may be 1, 2, 3, or 4, but is not limited thereto.

In Formula 1A, A₁ may be —CO₂M₁, —SO₃M₁, or —PO₃M₁M₂.

M₁ and M₂ may be each independently a hydrogen atom or an alkalinemetal, such as Li, Na, or K.

The substituent suggested by Formula 1A may be, but is not limited to, asubstituent represented by one of the Formulae 10A to 10E below:

In Formulae 10A to 10E, M₁ is H, Li, Na, or K.

The ionic polymer in the electron extraction layer 106 may include atleast one of a repeating unit represented by Formula 2A below, arepeating unit represented by Formula 3A below, a repeating unitrepresented by Formula 4A below, a repeating unit represented by Formula5A below, a repeating unit represented by Formula 6A below, and arepeating unit represented by Formula 7A below.

In Formulae 2A to 7A, Ar₁ to Ar₃ may be each independently a C₁-C₃₀alkylene group, a C₆-C₃₀ arylene group (for example, a phenylene group,a naphthylene group, an anthrylene group, a fluorenylene group, aspiro-fluorenylene group, or the like), a C₃-C₃₀ heteroarylene group(for example, a thiophenyl group, a pyrrolylene group, or the like), aC₅-C₃₀ cycloalkylene group (for example, a cyclohexylene group, or thelike), a C₁-C₃₀ alkylene group substituted with at least one firstgroup, a C₆-C₃₀ arylene group substituted with at least one second group(for example, a phenylene group, a naphthylene group, an anthrylenegroup, a fluorenylene group, or a spiro-fluorenylene group, which aresubstituted with at least one second group, or the like), a C₃-C₃₀heteroarylene group substituted with at least one third group (forexample, a thiophenyl group or a pyrrolylene group, which aresubstituted with at least one third group, or the like), or acycloalkylene group substituted with at least one fourth group (forexample, a cyclohexylene group substituted with at least one fourthgroup, or the like).

b to d may be each independently an integer from 1 to 20.

R₁ to R₄, R₁₁, R₁₃, R₁₄, R₁₅, the first group, the second group, thethird group, and the fourth group may be each independently a hydrogenatom (H), a nitro group (—NO₂), a cyano group (—CN), a hydroxyl group(—OH), a halogen atom, a substituted or unsubstituted C₁-C₃₀ alkylgroup, a substituted or unsubstituted C₁-C₃₀ alkoxy group, a substitutedor unsubstituted C₆-C₃₀ aryl group, a substituted or unsubstitutedC₆-C₃₀ arylalkyl group, a substituted or unsubstituted C₆-C₃₀ aryloxygroup, a substituted or unsubstituted C₂-C₃₀ heteroaryl group, asubstituted or unsubstituted C₂-C₃₀ heteroarylalkyl group, a substitutedor unsubstituted C₂-C₃₀ heteroaryloxy group, a substituted orunsubstituted C₅-C₂₀ cycloalkyl group, a substituted or unsubstitutedC₂-C₃₀ heterocycloalkyl group, a substituted or unsubstituted C₁-C₃₀alkylester group, a substituted or unsubstituted C₆-C₃₀ arylester group,a substituted or unsubstituted C₂-C₃₀ heteroarylester group, —N(Q₁)(Q₂),—C(═O)—NH₂, or a substituent represented by Formula 1A below, wherein Q₁to Q₂ are each independently a hydrogen atom, a C₁-C₃₀alkyl group, aC₆-C₃₀ aryl group, or a C₂-C₃₀ heteroaryl group, and at least one of R₁to R₄, R₁₁, R₁₃, R₁₄, R₁₅, the first group, the second group, the thirdgroup, and the fourth group may be a substituent represented by Formula1A above, which is described above, and will not be repeatedly describedhere.

The R₁ to R₄, R₁₁, R₁₃, R₁₄, R₁₅, the first group, the second group, thethird group, and the fifth group are each independently, but are notlimited to, a hydrogen atom, a C₁-C₁₀ alkyl group, a C₁-C₁₀ alkoxygroup, a phenyl group, a naphthyl group, an anthryl group, or asubstituent represented by Formula 1A above.

In some other embodiments, the ionic polymer may include a repeatingunit represented by Formula 8A below with a terminal to which thesubstituent represented by Formula 1A above is bound:

In Formula 8A, R₂₁ to R₂₄ may be each independently a hydrogen atom (H),a nitro group (—NO₂), a cyano group (—CN), a hydroxyl group (—OH), ahalogen atom, a substituted or unsubstituted C₁-C₃₀ alkyl group, asubstituted or unsubstituted C₁-C₃₀ alkoxy group, a substituted orunsubstituted C₆-C₃₀ aryl group, a substituted or unsubstituted C₆-C₃₀arylalkyl group, a substituted or unsubstituted C₆-C₃₀ aryloxy group, asubstituted or unsubstituted C₂-C₃₀ heteroaryl group, a substituted orunsubstituted C₂-C₃₀ heteroarylalkyl group, a substituted orunsubstituted C₂-C₃₀ heteroaryloxy group, a substituted or unsubstitutedC₅-C₂₀ cycloalkyl group, a substituted or unsubstituted C₂-C₃₀heterocycloalkyl group, a substituted or unsubstituted C₁-C₃₀ alkylestergroup, a substituted or unsubstituted C₆-C₃₀ arylester group, asubstituted or unsubstituted C₂-C₃₀ heteroarylester group, —N(Q₁)(Q₂),or —C(═O)—NH₂, wherein Q₁ to Q₂ are each independently a hydrogen atom,a C₁-C₃₀ alkyl group, a C₆-C₃₀ aryl group, or a C₂-C₃₀ heteroaryl group.Formula 1A is described above, and will not be repeatedly describedhere.

The ionic polymer may be a homopolymer including only one repeatingunit, for example, from among the repeating units represented by Formula2A. In another embodiment, the ionic polymer may be a copolymerincluding two different repeating units, for example, from among therepeating units represented by Formula 2A. In another embodiment, theionic polymer may be a copolymer, for example, including a repeatingunit represented by Formula 2A and a repeating unit represented byFormula 3A. The ionic polymer is not limited to the above, and may be inany form within the range described above.

The ionic polymer of the electron extraction layer 106 may berepresented by one of Formulae 30A to 30L below, but is not limitedthereto:

In Formulae 30A to 30L, n, n₁, and n₂ may be each independently aninteger from 10 to 1,000,000; and M₁ may be H, Li, Na, or K.

The ionic polymer may have a weight average molecular weight (Mw) offrom about 1,000 to about 90,000,000, and in some embodiments, may havea M_(W) of from about 10,000 to about 100,000. When the weight averagemolecular weight of the ionic polymer is within these ranges, themixture for forming the electron extraction layer 106 may be improved inrespect to coating property, viscosity, and flowability, so that theelectron extraction layer 106 may have improved interfacialcharacteristics.

The electron extraction layer 106 may have a thickness of about 0.1 nmto about 10 nm, and in some embodiments, may have a thickness of about 1nm to about 4 nm. When the thickness of the electron extraction layer106 is within these ranges, a vacuum energy level shifting effect asillustrated in FIG. 2 may be obtained without an increase in drivingvoltage.

The electron extraction layer 106 may be formed by forming a first layerfrom a mixture of the ionic polymer and a solvent; and removing at leastpart of the solvent from the first layer to obtain the electronextraction layer. In other words, the electron extraction layer 106 maybe formed by a so-called “wet process.”

The solvent may be a material that does not react with the ionic polymerto be included in the electron extraction layer 106 but is miscible withthe ionic polymer, and that may be readily removed by, for example,heat. In some embodiments, the solvent may be an alcohol, for example,ethyl alcohol, but is not limited thereto.

The first layer may be formed in a region where the electron extractionlayer 106 is to be formed, from the mixture of the ionic polymer and thesolvent. For example, the first layer may be formed on the photoactivelayer 104.

The first layer may be formed using any known method, for example, usingspin coating, inkjet printing, nozzle printing, dip coating,electrophoresis, tape casting, screen printing, doctor blade coating,gravure printing, gravure offset printing, a Langmuir-Blodgett method,or a layer-by-layer self-assembly method.

At least part of the solvent may be removed from the first layer, whichis formed from the mixture of the ionic polymer and the solvent, byusing any known method. In some embodiments, at least part of thesolvent may be removed from the first layer by thermal treatment, vacuumdrying or UV treatment. The resulting electron extraction layer 106 mayinclude the ionic polymer.

As described above, the electron extraction layer 106 may be formedusing a wet process. An organic solar cell including the electronextraction layer 106 formed as described above may have relatively lowcost as compared to an organic solar cell including an electronextraction layer formed using a deposition method that needs anexpensive vacuum chamber, evacuation equipment, or the like. When theelectron extraction layer 106 is formed using such a wet process, thephotoactive layer 104 underlying the electron extraction layer 106 mayhave minimized damage or may not be damaged, which may increase a fillfactor of the organic solar cell.

The second electrode 108 may be disposed on the electron extractionlayer 106. In one embodiment, the second electrode 108 may be “directly”disposed on the electron extraction layer 106, so that one surface ofthe electron extraction layer 106 directly contacts one surface of thesecond electrode 108 (see FIG. 1). In other words, an electron transportlayer, for example, a LiF layer formed by deposition, may not bedisposed between the electron extraction layer 106 and the secondelectrode 108.

The second electrode 108 may be a cathode. The second electrode 108 maybe formed using a low work-function material to facilitate migration ofelectrons from the photoactive layer 104. Non-limiting examples of amaterial for the second electrode 108 include metals such as aluminum,magnesium, calcium, sodium, potassium, indium, yttrium, lithium, silver,lead, and cesium, and a combination of at least two thereof.

As used herein, “*” indicates a binding site with a neighboring elementor repeating unit, which would be understood to one of ordinary skill inthe art.

One or more embodiments of the present invention will now be describedin detail with reference to the following examples. However, theseexamples are not intended to limit the scope of the one or moreembodiments of the present invention.

EXAMPLES Example 1

Poly(3,4-ethylenedioxythiophene):Poly(4-styrenesulfonate) (PEDOT:PSS)(CLEVIOS PH, available from H. C. Starck) was spin-coated on an ITOsubstrate (a glass substrate coated with ITO), and then thermallytreated at about 200° C. for about 10 minutes to form a hole extractionlayer having a thickness of about 35 nm. A mixture of1,2-dichlorobenzene, PCBM and P3HT (PCBM:P3HT=1:1 by weight) was stirredat about 60° C. for about 8 hours and then cooled to room temperature.The resultant mixture was spin-coated on the hole extraction layer andthen thermally treated at about 150° C. for about 30 minutes to form aphotoactive layer having a thickness of about 210 nm. Subsequently, amixture of poly(2,5-bis(3-sulfonatopropoxy)-1,4-phenylene disodiumsalt-alt-1,4-phenylene) (Product No. 659223, available fromSigma-Aldrich Co.) of Formula 30A (M₁=Na) and water was spin-coated onthe photoactive layer, and then thermally treated at about 50° C. forabout 10 minutes to form an ionic polymer-containing electron extractionlayer having a thickness of about 2.7 nm. Then, Al was deposited on theelectron extraction layer to form a second electrode having a thicknessof about 100 nm, thereby completing the manufacture of an organic solarcell.

Comparative Example 1

An organic solar cell was manufactured in the same manner as in Example1, except that the ionic polymer-containing electron extraction layerwas not formed.

Evaluation Example 1

Voltage-current density characteristics of the organic solar cells ofExample 1 and Comparative Example 1 were evaluated. The results areshown in FIG. 3. The voltage-current density characteristics of eachorganic solar cell were evaluated while irradiating a light of 100mW/cm² onto the organic solar cell with a Xenon lamp as a light source(the AM 1.5 solar spectrum of the Xenon lamp was corrected using astandard solar cell).

A short circuit current (J_(SC)), an open circuit voltage (V_(OC)), afill factor (FF), and a photoelectric conversion efficiency (PCE, %)were calculated using the voltage-current density graph. The results areshown in Table 1 below.

TABLE 1 Electron Open cir- Short cir- Fill Photoelectric extrac- cuitcuit cur- factor conversion tion voltage rent (J_(SC)) (FF) efficiencylayer (V_(OC)) (mV) (mA/cm²) (%) (PCE) (%) Compar- — 501 10.9 59.6 3.3ative Example 1 Example 1 Ionic 534 11.0 62.3 3.7 polymer of For- mula30A (M₁ = Na)

Referring to Table 1, the organic solar cell of Example 1 with theelectron extraction layer including the ionic polymer was found ashaving better characteristics as compared with the organic solar cell ofComparative Example 1.

The organic solar cell of Example 1 has an improved photoelectricconversion efficiency, and may be readily implemented as a thin film atlow cost.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

What is claimed is:
 1. An organic solar cell comprising: a firstelectrode; a second electrode; a photoactive layer disposed between thefirst electrode and the second electrode; and an electron extractionlayer disposed between the photoactive layer and the second electrode,wherein the electron extraction layer comprises an ionic polymer and isa dipole layer including a positive charge region (δ+) and a negativecharge region (δ−) within the electron extraction layer, wherein theionic polymer is represented by Formula 30A below:

wherein n₁ is an integer from 10 to 1,000,000, and M₁ is H, Li, Na or K.2. The organic solar cell of claim 1, wherein the ionic polymer has aweight average molecular weight (Mw) of from about 1,000 to about90,000,000.
 3. The organic solar cell of claim 1, wherein the electronextraction layer has a thickness of from about 0.1 nm to about 10 nm. 4.The organic solar cell of claim 1, wherein one surface of the electronextraction layer and one surface of the second electrode contact eachother.
 5. A method of manufacturing an organic solar cell, the methodcomprising: forming a first electrode on a substrate; forming aphotoactive layer on the first electrode; forming an electron extractionlayer comprising an ionic polymer on the photoactive layer; and forminga second electrode on the electron extraction layer, wherein the formingof the electron extraction layer comprises forming a first layer from amixture of the ionic polymer and a solvent; and removing at least partof the solvent from the first layer to obtain the electron extractionlayer, wherein the electron extraction layer is a dipole layer includinga positive charge region (δ+) and a negative charge region (δ−) withinthe electron extraction layer, wherein the ionic polymer is representedby Formula 30A below:

wherein n₁ is an integer from 10 to 1,000,000, and M₁ is H, Li, Na or K.6. The method of claim 5, wherein the forming of the first layer in theforming of the electron extraction layer is performed using spincoating, inkjet printing, nozzle printing, dip coating, electrophoresis,tape casting, screen printing, doctor blade coating, gravure printing,gravure offset printing, a Langmuir-Blogett method, or a layer-by-layerself-assembly method.